predictors: Make speculative_prefetch_predictor work with PlzNavigate

chrome/browser/predictors/resource_prefetch_common.h

Index: chrome/browser/predictors/resource_prefetch_common.h
diff --git a/chrome/browser/predictors/resource_prefetch_common.h b/chrome/browser/predictors/resource_prefetch_common.h
index afbd9240545ce0846f09f6818db313f583d4ee85..e293817e62123fb820d31f7a153e8cf8b167b37d 100644
--- a/chrome/browser/predictors/resource_prefetch_common.h
+++ b/chrome/browser/predictors/resource_prefetch_common.h
@@ -8,6 +8,8 @@
 #include <stddef.h>
 
 #include "base/time/time.h"
+#include "chrome/browser/sessions/session_tab_helper.h"
+#include "components/sessions/core/session_id.h"
 #include "url/gurl.h"
 
 class Profile;
@@ -43,17 +45,15 @@ struct NavigationID {
                const GURL& main_frame_url,
                const base::TimeTicks& creation_time);
   NavigationID(const NavigationID& other);
+
   bool operator<(const NavigationID& rhs) const;
   bool operator==(const NavigationID& rhs) const;
 
-  bool IsSameRenderer(const NavigationID& other) const;
-
   // Returns true iff the render_process_id_, render_frame_id_ and
   // frame_url_ has been set correctly.
   bool is_valid() const;
 
-  int render_process_id;
-  int render_frame_id;
+  SessionID session_id;

[Benoit L, 2016/12/19 16:55:55]

Looking at the code of SessionID, merely constructing a SessionID increases the
value of the next one (in the constructor).

Can you store a SessionID::id_type instead?

It is an int32_t, and I don't think we risk any wraparound issue here, but
perhaps some code somewhere doesn't expect it to increase really fast. Keeping a
SessionID here would create a new one for each request, at least.

Also, it makes the construction  (and copying) of NavigationID subtly
not-threadsafe.

Finally, it matches the return type of

static SessionID::id_type IdForTab(const content::WebContents* tab);

   GURL main_frame_url;
 
   // NOTE: Even though we store the creation time here, it is not used during